Acoustical panels with spaced layers



a 9 1966 J. MARCH 3,265,154

ACOUSTICAL PANELS WITH SPACED LAYERS Filed July 9, 1964 INVENTOR. JOHN d. M41677 United StatesPatent O ACOUSTICAL PANELS VVITH SPACED LAYERS John March, ()ld Brookville, N.Y., assignor to Insul- Coustic Corporation, Maspeth, N.Y.

Filed July 9, 1964, Ser. No. 381,331 '7 Claims. (Cl. 181-33) The'instan't invention relates to acoustical structures andmore particularly to an acoustical structure comprisinga plurality of layers of sound absorbing material, each adapted for absorbing sound in differing frequency ranges with the differing materials being laminated in layers with at least one of said layers being relatively stiff and having a dimpled surface providing the dual functions of being decorative and acting as a spacer to provide an air space when thestructure is used behind a perforated surface.

Sound absorbing materials find Widespread use in home, factory and oflice building structures where it is desired to reduce the amount of noise due to reverberation in such rooms. As another typical application, acoustic, or sound absorbing materials,- are used in air conditioning and ventilations systems of building structures. Insuch instances air is supplied or exhausted from individual rooms through the ducts and may carry noise from the air conditioning and ventilating equipment into these rooms. Other sounds, voices, etc. are also carried through the ducts connecting adjacent rooms and it is highly desirable to absorb these sounds in order to achieve'the desiredprivacy between rooms. It is therefore typical to provide such sound absorbing materials in the'ducts to provide such acoustical isolation, as well as providing sound absorbing materials for the room itself in order to substantially reduce the reflection of sound (i.e., the bouncing of sound waves) off thewalls and ceiling of the room.

In all of the above applications, it has been typical to provide a different type of material and structure to meet each individual situation thus greatly increasing the cost in complexity problems of the'manufacturer due to the requirement for providing such a variety of structures.

It is an object of the instant invention to provide a novel sound absorbing structure which lends itself readily and provides excellent operatingcharacteristics for all of the above applications by means of the integration of the characteristics of excellent sound absorbing qualities over a wide frequency range and having the stiffness and supporting strength required in these applications, as well as providing a decorative appearance which is desirable in certain of the above applications.

The instant invention is a sound absorbing structure substantially in sheet form and comprised of a plurality of layers of sound absorbing material with each layer being of a different density and being laminated to one another. At least one of said layers is of a relatively high density and stiffness and has the exposed surface thereof provided with a plurality of dimples or domeshaped projections, arranged across the surface of the layer in either a random or a regular fashion. All of the dome-shaped projections are substantially identical in dimensions and configuration and serve the multiple functions of providing a decorative arrangement; increasing the effective surface area for the treatment of sound waves to perform the absorption functions; as well as providing support means, which function is required when the pad of the invention is used as an absorbent structure Patented August 9, 1966 behind perforated metal ceilings in certain ones of the above mentioned applications.

Each of the layers in the sound absorbing structures is preferably, but not limitatively formed of a fiber glass material that is of glass fibers of predetermined diameters which are bonded together by a suitable binder material and are compressed so as to provide a substantially uniform density throughout the layer. Glass fiber diameter dimensions and layer densities of each layer may be varied in accordance with the needs of the user. By varying fiber diameter and density, these factors have direct relationship to the prequency ranges-which the layer will most effectively absorb. Thus, in the case where it is desired to absorb sound over a tide frequency range, this may be very easily done by selecting layers which have excellent sound absorbing properties over differing (and overlapping) frequency ranges and forming each of these layers to the other to provide a composite structure which has excellent sound absorbing characteristics over an extremely wide frequencyrange. Conversely, if-it is desired to absorb frequencies over a wide frequency range'and to pass sound frequencies Within a predetermined frequency range, this may also be done by selecting layers having excellent sound absorbing properties in the frequency ranges which it is desired to suppress and to eliminate, so to speak, the layer which might normally be selected for the frequency range which it is desired to pass. I

By selecting at least one layer for the sound absorbing structure which has a relatively high density so as to provide it with suitable stiffness and ridigity, this yields a sheet-like structure having one exposed surface, which when dimpled in addition to providing a decorative surface, further provides a surface (due to its density) which lends itself readily to being painted in cases where it is desired to provide such a structure in any color which may be desired by the user. The specific density of the exposed surface markedly reduces the amount of paint which the surface will absorb and thereby making it a structure suitable for painting. Since the use of the buttons or dimples increases the effective surface area of the sound absorption structure, this provides a very significant improvement in sound absorption characteristics over structures having no such buttons and, byincreasing the number of such buttons or dome-shaped projections employed in either a regular or a random fashion, the effective surface area may be increased to any desired amount.

While sound absorbing structures of the type designed in accordance with the principles of the instant invention are normally produced in substantially large sized sheets and due to their flexibility and the wide variety of applications for which such sheets may be employed, it is typical that the ultimate consumer will find it necessary to cut the sheets to varying dimensions in order that the sheets may be uniquely arranged to suit the purposes for which the material has been selected. It is therefore necessary that'astructure be provided which lends itself readily to being cut to form various patterns and configurations Without affecting the form or properties of the structure. This may be done readily with the structure of the instant invention in that the single stiff layer enables the structure to be easily out.

An alternative embodiment of the instant invention is comprised of at least two of the layers previously mentioned, i.e., a stiff layer and a layer of relatively less density and having a third layer comprising a septum sandwiched between the low and high density layers. The septum, which may be a light foil or a solid mass, such as a metal mesh, wire cloth, screening and the like, acts as a reflective medium for sound waves. In some cases sound waves impinging upon a sound absorbing structure will not be totally absorbed, but certain of the sound waves will be transmitted through such a structure. By the employment of a septum, any sound Waves impinging upon the surface of either the low or high density layers will be transmitted through that layer and will then impinge upon the septum. The septum acts to reflect the waves at substantially the same angle so that the angle of incidence is substantially equal to the angle of reflection. In doing so, the sound Wave which will preferably impinge upon the high density layer will thereby effectively pass through the high density layer twice, thereby greatly increasing the sound absorption properties of the structure.

By employing a septum of a predetermined thickness,

it is possible to cause the septum to vibrate or resonate at the frequency of the impinging sound waves and in so doing to absorb an extremely large percentage of the impinging sound wave energy. This action has been possible by providing a septum having a thickness of approximately two mils. Some materials which have proven successful are aluminum foil, vinyl and other wire mesh screens having a thickness of the order of two mils. The above structures provide a high density surface that effectively prevents air erosion of the fibers comprising the structure. Such air erosion is caused by the movement of air through and around the sound absorbing structure which, in fact, may carry away or erode a structure. By providing such a high density layer, this prevents lair erosion of the structure. Likewise, by providing the increased surface area through the dome-shaped projections, the absorption qualities of the sound absorbing structure is greatly enhanced. By employing a septum layer in the sound absorbing structure, the sound absorbing qualities may still be further enhanced. The septum also serves the further function of providing greater rigidity for the sound absorbing structure.

It is therefore one object of the instant invention to provide a novel sound absorbing structure.

Still another object of the instant invention is to provide a novel sound absorbing structure being comprised of a plurality of layers of sound absorbing material.

Another object of the instant invention is to provide a novel sound absorbing structure being formed of a plurality of layers of sound absorbing material each having excellent sound absorbing properties over differing frequency ranges.

Still another object of the instant invention is to provide novel sound absorbing structures being comprised of a plurality of layers of sound absorbing material of differing fiber diameters.

Still another object of the instant invention is to provide a novel sound absorbing structure being formed of a plurality of layers of sound absorbing material of differing fiber diameters and densities.

Another object of the instant invention is to provide a novel sound absorbing structure comprised of a plurality of layers of sound absorbing material being formed to one another.

Another object of the instant invention is to provide a novel sound absorbing structure comprised of a plurality of layers of sound absorbing material being formed to one another wherein at least one of said layers has a relative stiffness providing it with substantial rigidity and strength.

Another object of the instant invention is to provide a novel sound absorbing structure comprised of a plurality of layers of sound absorbing material being formed to one another wherein at least one of said layers has a relative stiffness providing it with substantial rigidity and strength and wherein the surface of said relatively stiff layer is provided with dimples for the multiple functions of providing a decorative structure, for providing suitable spacing between the surface of the stifi layer and an adjacent structure, as well as greatly increasing the surface area of the sound absorbing structure, thereby greatly increasing its sound absorbing properties.

Still another object of the instant invention is to provide a novel sound absorbing structure comprised of a plurality of layers of sound absorbing material being formed to one another and having a septum positioned between at least two of said layers for reflecting sound waves impinging upon the septum.

Still another object of the instant invention is' to provide a novel sound absorbing structure comprised of a *plurality of layers of sound absorbing material being formed to one another and having a septum positioned between at least two of said layers for absorbing sound waves impinging upon the system.

Another object of the instant invention isto provide a novel sound absorbing structure. wherein said septum is a metal-lie screen.

Another object of the instant invention is to provide a novel sound absorbing structure wherein said septum is a metallic foil.

Another object of the instant invention is to provide a novel sound absorbing structure wherein said septum is a plastic sheet.

These, and other objects of the instant invention will become apparent when reading the accompanying description and drawings in which:

FIGURE 1 is a perspective view showing a sound absorbing structure designed in accordance with the principles of the instant invention.

FIGURE 2 is a perspective view showing one possible application of the sound absorbing structure of the instant invention.

FIGURE 3 is a sectional view of an alternative em-' bodiment of the instant invention.

Referring now to the drawings, a sound absorbing structure 10 is comprised of first and second layers 11 and 12 of sound absorbing material.

The layer 12 may, for example, be formed of glass fibers bound together with a suitable binder material.

Typical fiber diameters are prefer-ably 0.00022". The binder employed is a phenolic resin binder representing 20% by weight of the total weight of the layer 12. It is preferably 1" thick and has a density of 1.1 lbs. per cubic ft. Layer 12 is normally referred to as the light density layer in the structure of FIGURE 1 and is designed so as to have excellent absorbing properties over a frequency range lying in the lower portion of the audio frequency range.

The layer 11 is preferably formed of glass fibers having a fiber diameter of 0.00015", which are bound to gether by a binder material representing 18% by weight of the total weight of layer 11. One binder material which has been shown to provide the requisite binding properties is a binder material comprised of by weight of urea and 20% by weight of water. While this binder has been shown to have good binding properties, it should be understood that any other suitable binding material may be employed in its place and the particular binding material selected lends no novelty tothe instant invention.

The density of layer 11 is preferably 4 lbs. per cubicof the audio frequency range. By combining the light and .heavy density layers 12 and 11, respectively, into the structure 10, this provides an over-all arrangement having excellent sound absorbing properties extending over the frequency -nange substantially from 80 to 6000 c.p.s. Experimentation has .shown the sound absorption coefiicient of the acoustical structure to lie substantially above 0.75 sabine over the frequency range cited above.

The layers Hand 12 are preferably formed independently of one another and are subsequently laminated to one another in any suitable manner along the interface 13. One lamination procedure may be that of providing suitable heat and pressure sufficient to provide a physical bond along the inner face 13. The bonding means, or processes employed may vary and the layers may event be joined together by suitable adhesive means with the ultimate bonding medium being selected dependent upon the needs of the user and therefore lending no novelty to the structure of the instant invention.

The exposed surface 14 of heavy density layer 11 is provided with a plurality of dome-shaped projections or dimples 15 which are preferably randomly positioned along the surface 14. While random spacing may be used, it should be understood that any'other (for example, regular) spacing may be employed. The dimples provide the surface 14 with a unique decorative appearance, as well as providing a spacing and supporting function which will best be understood from a description of the .arrangemetnt shown in FIGURE 2.

Whereas the embodiment shown in FIGURE 1 is comprised of two layers 11 and 12 of heavy and light density, respectively, it should be understood that the structure may be comprised of three or more layers which are laminated to one another in the same manner as described above with respect to the layers 11' and 12. Each of the layers, whether two or more such layers be employed, may likewise be formedof differing densities and in the 'case where only two layers are employed, such as that shown in FIGURE 1, the characteristics provided above are by no means to be interpreted in a limited sense, but may depart widely from the given specifications depending upon the frequency range or ranges which it is desired to absorb. The lamination or formation operation takes place in one step, thus, the two or morelayers making up the soundabsorbing structure are formed together and the tongue-shaped projection 15 are formed as well in the one operation. The economics of this operation makes it possible to take full advantage of a mass produced material which iswidely available such as, for example, fiberglass and to combine it with a special material in order to obtain the maximum economic advantage therefrom.

The stiffness of the high density layer 11 causes the over-all structure to be extremely dimensionally stable and very easy to work with. Since such structures 10 are preferably, but not necessarily formed in substantially large sheets with one typical size being 35" x 72" the ultimate consumer norm-ally requires that such sheets be easy to cut in order to be conformable to the specific use of the consumer. The high density layer makes the cutting, workability and handling of the sheets 10 very advantageous even though the low density layers when prepared independently do not exhibit these properties.

One typical use for the structure 10 shown in FIGURE 1 is that of providing a decorative acousticalceiling and/ or Wall structure. The sheets 10 may be mounted or secured to the wall in any suitable manner such as an adhesive material with the surface 16 of the light density material making physical contact with the ceiling and with the surface 14 of the structure 10 being exposed to view. In order to provide a more aesthetic appearing sound absorbing structure, the surface 14, including the domeshaped projections or dimples 15, may be painted with any suitable interior paint so as to blend into the decor of the room or area in which the sound absorbing material is employed. The relatively high density of the layer 11 substantially reduces the amount of paint which the structure 10' absorbs so that the amount of paint needed to cover a surface area of the surface 14 will lie substantially within the range of the amount of paint to cover typical room ceilings not having the sound absorbing properties of the structure 10. The structure 10 may in a like manner be mounted upon walls as desired, to still further enhance the sound absorbing properties of the room within which it is used while at the same time lending a decorative air to the region.

Another typical application for the sound absorbing structure 16 is shown in FIGURE 2. In the arrangement 20 shown therein there is provided a sound absorbing structure 10 which is positioned behind a metallic sheet 21. The metallic sheet 21 is perforated with a plurality of apertures 22 so as to enable sound waves to readily pass through the sheet 21. Metallic sheets of the type shown in FIGURE 2 are typically used for wall and/ or partitioned structures as well as for covering ceilings. While structures of this type are so perforated for the purpose of enabling sound waves to pass therethrough very readily, it is further desirable in the case where such metallic perforated sheets are used in partition structures to absorb sound Waves passing through the perforated metallic sheet so as to prevent the sound waves from leaving the room from which they came and entering an adjacent room so as to create an undesirable situation of cross-talk therebetween. Thus, in such applications the dual functions of enabling sound to be readily passed through perforated sheets and to be significantly deadened once it has passed through the sheet are functions which must of necessity to be provided in such structures.

It is typical therefore to provide a sound absorbing structure immediately behind each perforated metallic sheet for the purpose of absorbing or deadening sound waves which pass through the sheet. In structures of this type it has been found extremely advantageous to space the sound absorbing material a predetermined disstance away from the surface of the perforated metallic sheet since this resulting air space greatly enhances and takes full advantage of the sound absorbing properties of the overall structure and it thus became necessary in prior art structures to provide some suitable means for spacing and maintaining the spacing between the sound absorbing structure and the perforated sheet. In cases where the spacing means are provided along the edges of the panel, this has the decided disadvantage of lacking any support in the intermediate region, thus failing to maintain the air space of substantial uniformity through the entire region. With the arrangement of the instant invention the dome-shaped projections, or dimples 15,

being randomly located over substantially the entire region of surface 14, act to provide the requisite uniform spacing over substantially the entire region of the surface 14. The dimples 15 make only an extremely small amount of surface contact with the inner surface of perforated sheet 21 so that substantially all of the sound impinging upon the sheet 21 will pass through the perforations 22 and be absorbed and hence deadened by the structure 10. The sound absorbing structure 10 may be positioned behind any other porous sheet members for sound absorbing functions, in a manner similar to that shown in FIGURE 2, with the particular sheet behind which they are positioned being dependent only upon the needs of the user. Such sheets which may likewise be provided as ceiling structures, may also be further provided with the sound absorbing structure 10 and spaced in the manner shown in FIGURE 2 by means of the dimples 15. In the application of FIGURE 2 and in applications similar thereto the structure 10 may be formed of a larger number of laminations having differing fiber dimensions and densities, again depending only upon the needs of the user.

FIGURE 3 shows an alternative embodiment of the instant invention which is comprised of basically the same high and low density layers 11 and 12 as the layers 11 and I12 of FIGURES .l and 2. However, in the embodiment 10' of FIGURE 3, a layer or septum 25 is employed, which septum is positioned between or sandwiched betweenthe layers 11 and 12. The septum 25 may, for example, be a metallic foil, such as aluminum foil; a wire cloth; a metal mesh; a metallic or plastic screen or any other suitable material having a fair degree of rigidity. The operation and advantages of the embodiment of FIGURE 3 are as follows:

Regardless of the particular application to which the embodiment 10 of'iFIGURE 3 is employed, let it be assumed that sound Waves impinge upon the surface of high density layer 11 in a direction shown by arrow 26. These sound waves are transmitted or passed through the high density layer 1111 where they impinge upon the surface of septum 25. Due to the rigidity and stiffness characteristics of septum 25, these sound waves are reflected ofi the surface in the direction of arrow 27, for example. This reflective action thereby causes the sound waves to be treated as though they had passed through a high density layer of the type of high density layer '11 which is twice the thickness of layer l11 shown in FIGURE 6. Thus, by the use of a septum 25 the high density layer 11 has twice the sound absorption qualities of the layer [11' of FIGURE 1.

It has been found that by selecting a septum of a predetermined thickness it is possible to have the septum vibrate, or resonate. Due to the impact of impinging sound waves, this vibration or resonance causes the septum 25 to absorb a tremendous amount of the sound energy in addition to the remaining sound waves which will be reflected from the septum or layer 25. It has been found that aluminum foil of approximately two mils thickness will provide such resonating action and that an embodiment of the type shown in FIGURE 3 greatly enhances the total sound absorption qualities of the structure 10. While metal screen and metal foil have been described herein as two preferred septum layers, it should be understood that any other suitable material, be it metal or plastic, will operate with the desired effectiveness and the materials described herein are in no sense to be considered as limitative.

It can be seen from the foregoing that the instant invention provides a novel acoustical structure in sheet form which is comprised of a plurality of layers of sound absorbing material, each having sound absorbing properties of differing frequency ranges. The structure is provided with at least one surface thereof of substantially high density and is provided with a pattern of domeshaped projections or dimples which provide the dual functions of acting as a decorative means and a spacing means, depending upon the use for which the structure is selected. When the sound absorbing structure employs a septum layer between the low and high density layers the sound absorption qualities can be more than doubled, thereby providing an extremely low cost sound absorbing structure having extremely good sound absorbing qualities.

While specific embodiments have been described herein, it should be understood that many alternatives and modifications may be made to the structure described herein without departing from the spirit of the instant invention.

What is claimed is:

i1. An acoustical structure in sheet form for absorbing sound waves moving through said structure; comprising a first layer of sound absorbing material having a first predetermined density; a second layer of sound absorbing material having a second predetermined density greater than said first density; means for laminating first surfaces of said first and second layers; the second surface of said second layer having a plurality of projections arranged in a predetermined pattern extending outward from said second surface; all of said projections being integral with said second layer and being equal in size; a septum layer being positioned between said first and in predetermined pattern extending outward from said second surface; all of said projections being integral with said second layer and being equal in size; a septum layer being positioned between said first and second layers for absorbing impinging sound waves to increase the sound absorbing proper-ties of said structure.

3. An acoustical structure in sheet form for absorbing sound waves moving through said structure; comprising a first layer of sound absorbing material having a first predetermined density; a second layer of sound absorbing material having a second predetermined density greater than said first density; means for laminating first surfaces of said first and second layers; the second surface of said.

second layer having a plurality of projections arranged in a predetermined pattern extending outward from said second surface; all of said projections being integral with said second layer and being equal in size; a septum layer being positioned between said first and second layers for reflecting impinging sound waves to increase the sound absorbing properties of said structure; said septum layer being a metallic sheet.

4. An acoustical structure in sheet form for absorbing sound waves moving through said structure; comprising a first layer of sound absorbing material having a first predetermined density; a second layer of sound absorbing material having a second predetermined density greater than said first density; means for laminating first surfaces of said first and second layers; the second surface of said second layer having a plurality of projections arranged in a predetermined pattern extending outward from said second surface; all of said projections being integral with said second layer and being equal in size; a septum layer being positioned between said first and second layers for reflecting impinging sound waves to increase the sound absorbing properties of said structure; said septum layer being a metallic screen.

5. An acoustical structure in sheet form for absorbing sound waves moving through said structure; comprising a first layer of sound absorbing material having a first predetermined density; a second layer of sound absorbing material having a second predetermined density greater than said first density; means for laminating first surfaces of said first and second layers; the second surface of said second layer having a plurality of projections arranged in a predetermined pattern extending outward from said second surface; all of said projections being integral with said second layer and being equal in size; a septum layer being positioned between said first and second layers for reflecting impinging sound waves to increase the sound absorbing properties of said structure; said septum layer being a metallic sheet having a thickness of approximately two mils.

6. An acoustical structure in sheet form for absorbing sound waves moving through said structure; comprising a first layer of sound absorbing material having a first predetermined density; a second layer of sound absorbing material having a second predetermined density greater than said first density; means for laminating first surfaces of said first and second layers; the second surface of said second layer having a plurality of projections arranged in a predetermined pattern extending outward from said second surface; all of said projections being integral with said second layer and being equal in size; a septum layer being positioned between said first and second layers for reflecting impinging sound waves to in:

crease the sound absorbing properties of said structure; said septum layer being a metallic screen having a thickness of approximately two mils.

7. An acoustical structure in sheet form for absorbing sound waves moving through said structure; comprising a first layer of sound absorbing material having a first predetermined density; a second layer of sound absorbing material having a second predetermined density greater than said first density; means for laminating first surfaces of said [first and second layers; the second surface of said second layer having a plurality of projections arranged in a predetermined pattern extending outward from said second surface; all of said projections being integral with said second layer and being equal in size; a septum layer being positioned between said first and second layers for reflecting impinging sound waves to increase the sound absorbing properties of said structure; said septum being a sheet of aluminum foil.

References Cited by the Examiner UNITED STATES PATENTS Weiss 181 33 Slidell 181-33 Slidell 18Il-133 Parkinson 181-3 3 Lemmerman 181- 33 Brisley et al. 18'1--33 Ki Maio et a1. 181-313 Hulse et a1. 1 81- 33 RICHARD B. WILKINSON, Primary Examiner.

LE-O SMILOW, Examiner. 15 R. S. WARD, Assistant Examiner. 

1. AN ACOUSTICAL STRUCTURE IN SHEET FORM FOR ABSORBING SOUND WAVES MOVING THROUGH SAID STRUCTURE; COMPRISING A FIRST LAYER OF SOUND ABSORBING MATERIAL HAVING A FIRST PREDETERMINED DENSITY; A SECOND LAYER OF SOUND ABSORBING MATERIAL HAVING A SECOND PREDETERMINED DENSITY GREATER THAN SAID FIRST DENSITY; MEANS FOR LAMINATING FIRST SURFACES OF SAID FIRST AND SECOND LAYERS; THE SECOND SURFACE OF SAID SECOND LAYER HAVING A PLURALITY OF PROJECTIONS ARRANGED IN A PREDETERMINED PATTERN EXTENDING OUTWARD 